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Description
The United State's Industrial Sector uses about thirty percent of the total U.S. energy use, and is responsible for about thirty percent of carbon dioxide emission. Many of the industrial processes require a large quantity of thermal energy of which a large portion is eventually exhausted to the environment. Recovering this waste heat offers the largest opportunity to reduce the U.S. manufacturing sector's energy use. The objective of this study is to establish an evaluation method that combines environmental impact of existing working fluids and their thermodynamic properties as they apply to ultra-low grade heat Organic Rankine Cycle (ORC). Global warming and ozone depleting potentials are used to evaluate the environmental impact of the most common working fluids as well as their toxicity and flammability. Physical properties are used to evaluate these fluids for ultra-low grade heat ORC application. With regard to the environmental impact, the preferable working fluids are Hydrofluorocarbons (HFCs) - which do not contain chlorine and do not damage the ozone layerand Hydrocarbons (HCs) - which naturally exists in nature. Considering both environmental and performance characteristics, based on this study, the preferable working fluids are 1,1,1,3,3- Pentafluoropropane (HFC-245fa), followed by 1,1,1,2-Tetrafluoroethane (HFC-134a), 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-Hexafluoropropane (HFC- 236ea), 1,1,1,3,3,3-Hexafluoropropane (HFC-236fa), Butane (HC-600), Isobutane (HC- 600a), Pentane (HC-601), and Isopentane (HC-601a). To develop a classifier that can predict the probability of any working fluid being a desirable candidate for ultra-low grade heat ORC, logistic regression analysis was used. The phase out year, ozone depleting potential, global warming potential, type of fluid, and critical temperature of the screened working fluids and above results were used to develop this classifier. With the help of this classifier any working fluid can be classified as a desirable or undesirable candidate for ultra-low grade heat ORC. This study makes it clear that none of the current working fluids have all the criteria for an ideal refrigerant. The Ozone depletion and climate change are global issues. However, the choice of alternative refrigerants is a domestic issue. Policy makers in each government should decide which characteristics of ideal working fluid should be neglected in order to maximize the efficiency of the recovered waste energy and reduce environmental impacts of emissions.
